VANADIUM IN OCTOPUS 215

INTRODUCTION

Vanadium is an element that, in recent years, hasattracted considerable environmental and scientificinterest because of its wide industrial applications,

large releases into the environment and complexchemistry (Nriagu, 1998). The concentration of dis-solved vanadium in seawater is typically 0.001-0.003mg/l (WHO, 1988, 2001) and both marine animalsand plants play an important role in its transfer. Vana-dium does not react chemically with seawater but iscontinuously removed by biochemical processes and

SCI. MAR., 69 (2): 215-222 SCIENTIA MARINA 2005

Vanadium, rubidium and potassium in Octopus vulgaris(Mollusca: Cephalopoda)*

SÓNIA SEIXAS 1 and GRAHAM J. PIERCE 2

1 Universidade Aberta, Rua Escola Politécnica, 147, 1269-001 Lisboa, Portugal. E-mail: sonia@univ-ab.pt2 Department of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, Scotland, United Kingdom.

E-mail: g.j.pierce@abdn.ac.uk

SUMMARY: The levels of vanadium, rubidium and potassium were determined in Octopus vulgaris caught during com-mercial fishing activities at three locations (Cascais, Santa Luzia and Viana do Castelo) in Portugal in autumn and spring.We determined the concentration of these elements in digestive gland, branchial heart, gills, mantle and arms in males andfemales. At least five males and five females were assessed for each season/location combination. Elemental concentrationswere determined by Particle Induced X-ray Emission (PIXE). Vanadium was detectable only in digestive gland andbranchial heart samples. Its concentration was not correlated with total weight, total length or mantle length. There were nodifferences in concentrations of V, Rb and K between sexes. There were significant differences in vanadium concentrationsin branchial hearts in autumn between samples from Viana do Castelo and those from the other two sites. We found a sig-nificant positive relationship between the concentration of vanadium and those of potassium and rubidium in branchialhearts. Branchial hearts appear to play an important role in decontamination of V.

Keywords: vanadium, rubidium, potassium, octopus, metals, pollution.

RESUMEN: VANADIO, RUBIDIO Y POTASIO EN OCTOPUS VULGARIS (MOLLUSCA: CEPHALOPODA). – Se determinaron los nivelesde vanadio, rubidio y potasio en Octopus vulgaris capturado durante las actividades pesqueras en tres localidades de Portu-gal (Cascais, Santa Luzia y Viana do Castelo). Las concentraciones de estos elementos se determinaron en la glándula diges-tiva, corazón branquial, branquias, manto y en los brazos de machos y hembras en otoño y primavera. Al menos cincomachos y cinco hembras se muestrearon para cada combinación de temporada/localidad. Las concentraciones de estos ele-mentos fueron determinadas por el método de Particle Induced X-ray Emission (PIXE). El vanadio fue solamente detecta-do en glándula digestiva y en los corazones branquiales y su concentración no tuvo correlación con el peso total, longitudtotal o longitud del manto. No se detectaron diferencias significativas en la concentración de V, Rb y K, entre machos yhembras aunque sí en las cantidades de vanadio acumulado en la glándula digestiva en otoño y primavera en muestras deCascais y Santa-Luzia. En el caso del V en los corazones branquiales, se encontraron diferencias significativas en el otoñoentre concentraciones en muestras de Viana do Castelo y las de las otras dos localidades. Se encontró una relación signifi-cativa positiva entre la concentración de vanadio y las de potasio y rubidio en los corazones branquiales. Concentracionesde Rb y K están correlacionadas en todos los tejidos excepto los musculares. Los corazones branquiales parecen jugar unpapel importante en la descontaminación del V.

Palabras clave: vanadio, rubidio, potasio, pulpo, metales, polución.

*Received May 26, 2004. Accepted October 15, 2004.

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by absorption. Invertebrates accumulate vanadiumprincipally through their diet (Miramand and Fowler,1998), and have high levels of vanadium when com-pared with vertebrates—in which the concentrationsare so low that detection is difficult.

Ascidians are known to accumulate vanadium intheir blood cells (vanadocytes) in concentrations of106 to 107 times those found in seawater (Kanda et al.,1997; Michibata and Kanamori, 1998) and they haveproteins, vanabins, which bind vanadium ions (Uekiet al., 2003). The reason for this accumulation is notknown (Nielsen and Uthus, 1994). However, vanadi-um concentrations in benthic invertebrates such asannelids, crustaceans, echinoderms and molluscs aregenerally low, with levels varying from 1 to 4 mg/kgdry weight (Miramand and Fowler, 1998).

Vanadium is an essential trace element for nitro-gen-fixing bacteria (WHO, 2001; Zaslavsky et al.,1999) but there is no consensus on its role in ani-mals. Some authors state that it has an unknownrole; other authors say that it is a non-essentialmetal. Vanadium is toxic to vertebrates even at lowconcentrations (Owusu-Yaw et al., 1990) and it isalso known to be toxic to invertebrates (e.g. larvaeof Crassostrea gigas; Fichet and Miramand, 1998)and fish (Chakraborty et al., 1998). In a study ongobies, Miramand et al. (1992) suggested that vana-dium does not bioaccumulate in the food chain.

Rubidium is widely distributed in nature. It hasno known biological role but is said to stimulate themetabolism. The only study to date on a molluscshowed it to be toxic to oysters (Salaun and Truchet,1996). In vertebrates, the metabolism of rubidium isclosely related to that potassium. Indeed, it has beensuggested that rubidium represents a nutritional sub-stitute for potassium (Bruce and Duff, 1968). How-ever, in oysters the rubidium metabolism clearly dif-fers from that of potassium (Salaun and Truchet,1996). Potassium is an essential element for allorganisms. Absorption by animals from the diet ispassive and does not require any specific mecha-nism. In vertebrates the kidneys are the main regu-lators of body potassium.

In several species, including humans, vanadium inthe form of vanadate (the +5 oxidation state), is a pow-erful inhibitor of Na,K-ATPase (Cantley and Aisen,1979). In rats, the inhibition of Na,K-ATPase causedby vanadate is dependent on the concentration ofpotassium (K) in muscle (Searle et al., 1983). There isevidence that, under appropriate conditions, K+ or itscongeners such as Rb+ become bound to Na,K-ATPase in a way that slows down its release. This type

of binding is called occlusion (Kaufman et al. 1999).Na,K-ATPase has the same apparent affinity for potas-sium and rubidium (Rb) ions because of its hydrolyticactivity (Cheval and Doucet, 1990). Vanadate opti-mises the occlusion of ATPase by rubidium (Rabon etal., 1993) because rubidium binds much better to theprotonated pump (form E2) than the unprotonatedpump (Blostein, 1985; Milanic and Arnett, 2002). Theintrinsic affinity of this enzyme for vanadate—and theinteraction between this element and both rubidiumand potassium—was demonstrated in an assay inwhich the enzyme was incubated with various con-centrations of vanadate in the presence of K+ or Rb+(Toustrup-Jensen and Vilsen, 2002).

The octopus (Octopus vulgaris) is a cephalopodmollusc with a high growth rate and a short life span.It is benthic and its diet is essentially composed ofbivalves, crustaceans, other cephalopods and fishes(Lee, 1994). O. vulgaris has a high economic and cul-tural value in Portugal, and is an important fisheryresource throughout southern Europe. Cephalopods,such as octopus, are known to bioaccumulate highlevels of certain metals, notably cadmium, and repre-sent an important route of transfer to top marinepredators, including humans (Bustamante et al.,1998). The present study examines levels of twopoorly documented metals, vanadium and rubidium,both potentially toxic, in O. vulgaris from the Por-tuguese coast. Given the known links between vana-dium, rubidium and potassium metabolism in ani-mals, potassium concentrations are also recorded.

To provide information on variation in concen-trations around Portugal, octopus were collected atthree sites on different parts of the Portuguese coast,all important fishing areas. In view of the short lifes-pan and sex-related differences in growth and matu-ration (Mangold, 1989), seasonal and sex-relateddifferences are also investigated. Previous work onlead levels in this species indicated differencesbetween the sexes (Seixas et al., 2002). Lastly, weanalyse the relationships between concentrations ofthe three elements and discuss the possible implica-tions of the observed levels and interactions for thehealth of the octopus and its predators.

MATERIAL AND METHODS

Sampling and sample preparation

Animals landed by commercial fisheries weresampled at three locations along the Portuguese

216 S. SEIXAS and G. PIERCE

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coast: (a) Viana do Castelo, situated in the north ofthe country, (b) Cascais in the centre, with a stronginfluence of the Tagus River (the largest river inPortugal), and (c) Santa-Luzia, situated in theAlgarve region on the south coast of Portugal. Ani-mals in these zones were sampled over two seasonsof the year, autumn (November, 1999) and spring(May, 2000). We sampled 60 octopuses: 10 animals(5 males and 5 females) in each season and eachzone.

Total length, mantle length, total weight, sex andmaturation state were determined for each animal.The maturation state was determined by directobservation of colours of reproductive structures(Gonçalves, 1993). The maturity index followsGuerra (1975), based on microscopic analyses andmeasurements of ovules and spermatophores.

The tissues collected for analysis were digestiveglands, branchial hearts, gills, mantles and arms.The tissue samples were stored frozen between -20oC and -40 oC prior to analysis. We could not analysethe samples of branchial hearts, gills, mantles andarms from Viana do Castelo in spring due to prob-lems that occurred during the storage of the samples.

Analytical procedure

The concentrations of vanadium, potassium andrubidium were determined using PIXE (ParticleInduced X - ray Emission). First we freeze-dried thesamples. This was followed by microwave aciddigestion with 9:1 v/v HNO3 and H2O2, 4 minutes at300 W. We used yttrium (Y) as the internal standard.After that, three aliquots of 10 µl of sample from eachanimal and tissue were analysed. The technique ofPIXE was available in a Van der Graff accelerator atthe Technological and Nuclear Institute of Portugal(ITN). Irradiation of the sample was made by a sheafof protons of 2.2 MeV with 5 mm diameter and 6.5nA mm-2 intensity in a vacuum. A MylarTM of 350 µm

thickness was used to eliminate the contribution of X-rays of low energy (lower than potassium). The crys-tal where the emission of X-ray was detected wasmade of Si(Li). For each X-ray detected one electri-cal signal was produced, which was processed in amulti-channel system (MCA). The spectra wereanalysed with the computer programs AXIL andDATTPIXE (International Atomic Energy Agency),which calculated the concentration of elements.

Detection limits were for V: 0.4 mg/kg, Rb: 1.28mg/kg, K< 0.0 mg/kg.

The results for each tissue are given relative todry weight of tissue (mg kg-1 dry weight - dw).

Statistical procedures

Statistical analysis of the data was carried outusing STATISTICA (StatSoft, Inc., 1995). We used3-way ANOVA (factors: sex, season and location)for elements in digestive glands and 2-way ANOVA(factors: sex and season; data missing for one loca-tion) for elements in branchial hearts. When signifi-cant variation was detected using ANOVA, Studen-t’s t-tests were used to identify where those differ-ences occurred. To analyse the correlations betweenstate of maturation (an ordinal variable) and concen-tration of elements, we used Spearman rank correla-tions. For quantifying relationships between otherparameters, such as total length, mantle length andtotal weight, and concentrations of elements, weused the Pearson coefficient of correlation.

RESULTS

The averages and standard deviations of weightsand total lengths of the animals from each samplinglocation and occasion are given in Table 1.

The body weights of the sampled animals dif-fered significantly between locations, being largest

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TABLE 1. – The average (± 1 standard deviation) of weights, total and mantle lengths and state of maturation of octopus for each sex, location and season.

Season Parameters Viana do Castelo Cascais SantaLuziaFemales Males Females Males Females Males

Autumn Weight (g) 1249 ± 231 1249 ± 304 1266 ± 660 1524 ± 628 3788 ±1480 3560 ± 676Total Length (mm) 870 ± 69 878 ± 140 872 ± 123 892 ± 120 1085 ± 185 1070 ± 125Mantle Length (mm) 154 ± 8 155 ± 11 154 ± 26 166 ± 29 224 ± 38 232 ± 18Maturation 2.3 ± 1.6 3.0 ± 0.0 2.1 ± 0.7 2.4 ± 0.9 2.0 ± 0.7 2.4 ± 0.9

Spring Weight (g) 939 ± 199 906 ± 249 2183 ± 424 1052 ± 314 2246 ± 807 3157 ± 2215Total Length (mm) 768 ± 65 758 ± 50 914 ± 61 746 ± 91 1020 ± 139 1073 ± 208Mantle length (mm) 134 ± 10 134 ± 11 192 ± 16 146 ± 17 189 ± 22 188 ± 36Maturation 2.1 ± 1.5 1.4 ± 0.5 2.8 ± 0.8 3.0 ± 0.0 2.0 ± 0.0 2.7 ± 0.6

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at Santa Luzia and smallest at Viana do Castelo(Viana/Cascais: t=-2.53, N=40, p=0.015; Viana/St.Luzia: t=-6.56, N=40, p=0.00; Cascais/St. Luzia: t=-4.97, N=40, p=0.00).

Vanadium was detected only in digestive glandsand branchial hearts. In gills, mantles and arms thelevels were lower than the detection limit (< 0.4mg/kg). Rubidium and potassium were detected inall tissues analysed.

There were no significant differences betweensexes in concentrations of any of the three elementsmeasured in the tissues analysed (Table 2). Hencethe data for both genders were treated together insubsequent analyses.

Vanadium

The concentrations and total amounts of vanadi-um in digestive glands and branchial hearts for sam-ples from each location-season combination areshown in Figure 1 and 2 respectively. The concen-

tration of vanadium in branchial hearts was marked-ly higher than in digestive glands (F=9.05, p=0.00),although estimated total amounts present were high-er in the latter organ. Concentrations in the two tis-sues were positively correlated with each other(r=0.38, N=50, p=0.04).

The concentration of vanadium in digestivegland was not significantly correlated with totallength, mantle length or wet weight of the animals.

218 S. SEIXAS and G. PIERCE

FIG. 1. – Concentration of vanadium in digestive glands and branchial hearts.

TABLE 2. – Results of ANOVA for effects of location, season and gender on concentrations of metals in digestive glands branchial hearts,gills, mantle and arms. The table shows the F values, followed by the associated number of samples (N) and probability (p) in parentheses.

Significant effects are shown in bold face.

Tissue Metal Gender Season Location

Digestive glands V 0.00 (60, 0.98) 4.17 (60, 0.048) 3.90 (60, 0.04)Rb 0.39 (60, 0.54) 2.40 (60, 0.13) 3.49 (60, 0.04)K 0.15 (60, 0.70) 12.49 (60, 0.00) 2.63 (60, 0.08)

Tissue Metal Gender Season Location (autumn) Location (spring)

Branchial V 3.21 (50, 0.08) 0.08 (50, 0.78) 9.10 (50, 0.00) 0.02 (50, 0.89)Hearts Rb 3.61 (50, 0.07) 1.18 (50, 0.28) 0.31 (50, 0.74) 0.08 (50, 0.78)

K 1.13 (50, 0.29) 0.36 (50, 0.55) 13.90 (50, 0.00) 0.15 (50, 0.71)Gills Rb 0.00 (50, 0.98) 0.00 (50, 0.96) 0.75 (50, 0.50) 2.44 (50, 0.13)

K 0.05 (50, 0.83) 2.95 (50, 0.09) 1.55 (50, 0.24) 5.51 (50, 0.02)Mantle Rb 1.13 (50, 0.30) 1.87 (50, 0.19) 0.13 (50, 0.88) 7.5 (50, 0.00)

K 2.11 (50, 0.15) 3.61 (50, 0.07) 0.01 (50, 0.99) 0.87 (50, 0.38)Arms Rb 0.73 (50, 0.40) 1.34 (50, 0.26) 2.76 (50, 0.10) 6.84 (50, 0.03)

K 0.01 (50, 0.93) 1.17 (50, 0.29) 7.22 (50, 0.01) 3.70 (50, 0.08)

FIG. 2. – Total amount of vanadium and rubidium in digestive glands and branchial hearts.

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There was a significant positive correlationbetween the maturation state and the concentrationof vanadium in digestive gland (R=0.35, N=60,p=0.03). However, vanadium concentration inbranchial hearts was not correlated with maturationstate and it should be noted that, since 24 differentcorrelation coefficients were computed (3 metals in2 tissues in relation to 4 biological variables), atleast one of them would be expected to be signifi-cant (P<0.05) by chance alone.

The ANOVA results on variation in concentra-tion of vanadium in relation to effects of locationand season are shown in Table 2 and, where signifi-cant variation was identified, the differences aresummarised in Table 3.

Significantly higher concentrations of vanadiumwere accumulated in digestive gland in spring than inautumn, for both Cascais and Santa-Luzia samples(Fig. 1). However, in the Viana do Castelo samples,there were no differences between seasons. The con-centrations in autumn and spring varied in relation tosample location. In autumn, levels of vanadium indigestive gland for Viana do Castelo were higher thanat the other two locations, while in spring levels werehigher at Cascais than at Viana do Castelo.

For the autumn branchial heart samples, there

were differences between the concentration of vana-dium in Viana and the other two places, the levelbeing higher in Viana.

Rubidium

Concentrations of rubidium were slightly (butnot significantly) higher in branchial hearts than inall other tissues (Fig. 3), although (as for vanadium)the total amount present in the digestive gland wasgreater than in the branchial hearts (Fig. 2). The con-centrations of Rb in digestive glands, branchialhearts, gills, mantles and arms were not correlatedwith each other.

Concentrations of rubidium in digestive glands,branchial hearts, gills, mantles and arms were notcorrelated with total length, mantle length, wetweight or maturation of the animals.

ANOVA results on variation in concentration ofrubidium in relation to locations and seasons areshown in Table 2 and, where significant variationwas identified, the differences are summarised inTable 3.

The levels of rubidium showed no differencesbetween seasons or locations for digestive glands,branchial hearts and gills; in mantles and arms therewere differences between locations in spring.

Potassium

In general, the concentrations of potassium werefairly similar in all studied tissues (Fig. 4).

Concentrations of K were correlated with biolog-ical parameters of the animals only in gills and arms:with total length (r=-0.40, N=50, p=0.01 and r=-0.39, N=50, p=0.03 respectively), mantle length(r=-0.33, N=50, p=0.04 and r=-0.43, N=50, p=0.01respectively) and wet weight (r=-0.39, N=50,

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TABLE 3. – Student’s t-test results for comparisons between the three locations (above) and the two seasons (autumn and spring) (bottom).The table shows the t values and associated probability (p) in parentheses. Significant differences are shown in bold face. These tests are used

to indicate which differences were significant if ANOVA showed that there was significant variation.

Tissue Element Season Viana/Cascais Viana/St. Luzia Cascais/St. Luzia

Digestive gland V Autumn 2.30 (0.04) 2.37 (0.03) 0.36 (0.73)Digestive gland V Spring -3.48 (0.01) -0.85 (0.42) 1.53 (0.15)Digestive gland Rb - -2.07 (0.048) -2.49 (0.02) -0.42 (0.69)Branchial heart V Autumn 3.72 (0.00) 2.20 (0.049) -0.52 (0.61)Branchial heart K Autumn 4.64 (0.00) 4.08 (0.00) 1.33 (0.20)Arms K Autumn 1.10 (0.29) 3.01 (0.02) 4.68 (0.00)

Tissue Element Viana Cascais St. Luzia

Digestive gland V 0.96 (0.36) -7.50 (0.00) -2.44 (0.03)Digestive gland K -0.20 (0.85) -3.03 (0.01) -1.37 (0.20)

FIG. 3. – Concentration of rubidium in tissues analysed.

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p=0.01 and r=-0.44, N=50, p=0.01 respectively).Concentrations of K were not correlated with matu-ration in any of the tissues analysed.

Concentrations of K in digestive glands werecorrelated with concentrations of K in branchialhearts, gills, mantles and arms (r=0.35, p=0.04;r=0.33, p=0.04; r=0.37, p=0.03; r=0.46, p=0.01respectively; N=50 in all cases). Concentrations ofK in arms were also correlated with those inbranchial hearts, gills and mantles (r=0.62, p=0.00;r=0.50, p=0.01; r=0.64, p=0.00 respectively; N=50in all cases).

ANOVA results on variation in concentration ofpotassium in relation to locations and seasons areshown in Table 2 and, where significant variationwas identified, the differences are summarised inTable 3. The levels of potassium in digestive glandsshowed statistically significant differences onlybetween seasons: in samples from Cascais, the lev-els were higher in spring.

In branchial hearts and arms, the concentrationsof potassium differed between locations in autumn.In branchial hearts levels were similar for Cascaisand St. Luzia, but the concentrations for both placeswere significantly lower than at Viana. In arms thelevels were similar at Viana and Cascais but thesetwo locations had higher values than St. Luzia.

Correlations between elements

For branchial hearts, there were positive correla-tions between the concentrations of vanadium andrubidium (r=0.32, N=60, p=0.02) and those of vana-dium and potassium (r=0.41, N=60, p=0.01). On theother hand, both graphs indicate a wide scatter ofdata and, as indicated by the r2 values, only around13 and 17% respectively of variation in rubidiumand potassium concentrations is explained by a lin-ear relationship with vanadium concentration.

Concentrations of Rb and K were positive corre-lated in digestive glands, branchial hearts and gills(r=0.70, N=60, p=0.00; r=0.60, N=50, p=0.00;r=0.58, N=50, p=0.00 respectively). In mantles andarms there was no correlation between Rb and K.

DISCUSSION

In Octopus vulgaris, we found that branchialhearts had higher concentrations of vanadium thandigestive glands. This is similar to the results ofMiramand and Guary (1980), who studied theMediterranean octopus. Miramand and Fowler(1998) found that branchial hearts in cephalopodsconstitute only 0.2% of the whole animal weight butcontain 1-6% of the total vanadium body burden.Higher concentrations of rubidium were also higherin branchial hearts than in other tissues.

We found higher total quantities of vanadium andrubidium in the digestive gland (as might be expect-ed given the relative size of these organs). In Sepiaofficinalis, vanadium in digestive glands represents40% of the total found in the animals (Miramandand Fowler, 1998).

In contrast to results for vanadium and rubidium,there were no consistent differences in potassiumconcentration between different organs.

In branchial hearts, the highest concentration ofvanadium was found in the samples from Viana inautumn; in other samples the levels varied between22 and 33 mg/kg. It can be suggested that the Vianaarea is more contaminated with vanadium thanother locations studied and, if so, that the contami-nation source is probably oil. During the summer,precipitation and riverine inputs are lower, so theaccumulation in coastal areas of pollutants such asoils (an important source of vanadium contamina-tion in the ocean, Crans et al., 1998) would be high-er, and this would be reflected in animals capturedin autumn. In winter, levels of precipitation andriverine inputs are higher and strongly influencecoastal conditions.

Values of V and K in digestive glands obtained inthis study are broadly similar to data from the liter-ature (Table 4). However, the highest concentrationof vanadium in digestive glands recorded in the pre-sent study, in the samples from Cascais in spring(10.1±2.92 mg kg-1 dw), is somewhat higher thanthe values for other cephalopod species in the litera-ture. Levels of Rb in digestive glands were a littlehigher than values found for other cephalopods.

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FIG. 4. – Concentration of potassium in tissues analysed.

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In branchial hearts, the level of V recorded atViana was very high compared with the values in theliterature. However, our results for other locationswere similar to values obtained in Monaco for thesame species (Table 4). In general, levels recordedin Octopus vulgaris are higher than those in othercephalopods. There are no reports in the literatureon Rb and K levels in branchial hearts.

Our data are consistent with the hypothesis ofMiramand and Fowler (1998) that branchial heartsplay an important role in accumulation and excre-tion of V. Vanadium is known to affect the func-tioning of the enzyme Na,K-ATPase: it convertsthis enzyme to the protonated state. Our resultsindicate relationships between the concentrations ofvanadium and potassium and between those ofvanadium and rubidium in branchial hearts. Itshould be noted that, in cephalopods, Na,K-ATPaseis responsible for the excretion of NH4

+ (Boucher-Rodoni and Mangold, 1994). Thus, if high vanadi-um levels adversely affect enzyme activity, theexcretion of ammonium may be affected. However,at present it is not known whether the concentrationof vanadium found in branchial hearts is sufficientto induce alterations in concentrations of potassiumand rubidium or to have deleterious effects on octo-pus health.

In octopus we do not yet know the effects ofvanadium. In human beings, problems with theenzyme Na,K-ATPase, associated with high levelsof potassium and vanadium, can cause heart dis-eases and hypertension (IPCS, 1990). The cardiac

cycle and the pressure volume loops of the systemicheart of Octopus vulgaris are functionally not dis-similar to those described in mammals (Berne andLevy, 1992 in Agnisola and Houlihan, 1994).

The correlations between concentrations of Rband K in all tissues with the exception of muscle(mantles and arms) could indicate a relationshipbetween them. However, further evidence is needed.

Another aspect that may be considered is thatOctopus may be one of the species responsible for thebioaccumulation of vanadium in higher trophic lev-els. Cephalopods are regarded as being an importantlink in marine food chains (Piatkowski et al., 2001).

Studies on bioaccumulation of vanadium in pin-nipeds (northern fur seal Callorhinus ursinus;Steller’s sea lion Eumetopias jubatus; harbour sealPhoca vitulina; and ribbon seal Phoca fasciata)caught in the northern Pacific show high concentra-tions in liver, hair and bone (Saeki et al., 1999).High levels of V were reported in liver of marinemammals captured in Alaska after they were sub-jected to oil contamination over a long period oftime (Mackey et al., 1996), although these levelsremained lower than those measured in the tissues ofcephalopods, especially branchial hearts.

Given increasing scientific interest in vanadiumand considering that cephalopods have a high eco-nomic value and represent an important path fortransfer of contaminants to top predators in marinefood webs, further studies on vanadium levels areneeded. The relationships between vanadium, rubid-ium and potassium also deserve further attention.

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TABLE 4. – Concentration of V, Rb and K (mg/kg dw) in digestive glands and branchial hearts as found in the present study and the studieson cephalopods. [*Values that refer to wet weight.] (In the present study, ratios of wet weight to dry weight were 2.3 in digestive gland and

4.4 in branchial hearts).

Locations V Rb K Authors

Digestive GlandOctopus vulgaris Viana do Castelo 7.2 ± 6.9 5.0 ± 2.5 6173 ± 942 Present study

Cascais 6.5 ± 4.7 6.8 ± 2.2 7747 ± 2257 Present studySanta Luzia 5.0 ± 5.1 7.1 ± 1.8 7125 ± 1861 Present study

Monaco 4.5 ±1.0 Miramand and Guary (1980)Eledone cirrhosa English Channel 3.3 ± 0.5 Miramand and Bentley (1992)Todarodes pacificus Pacific coast 5.5* 1.5* 4900* Ichihashi et al. (2001b)

Sea of Japan 0.22* 1.1* 3600* Ichihashi et al. (2001b)Nemuro Strait 0.66* 0.91* 2700* Ichihashi et al. (2001b)

Stenotheuthis oualaniensis Japan 0.74 0.54 4450 Ichihashi et al. (2001a)Sepia officinalis English Channel 5.0 ± 1.3 Miramand and Bentley (1992)

Nautilus macromphalus New Caledonia 8.8 ± 2.0 Bustamante et al. (2000)

Branchial heartsOctopus vulgaris Viana do Castelo 53.0 ± 25.4 9.5 ± 2.9 8946 ± 1627 Present study

Cascais 27.5 ± 11.0 9.4 ± 2.5 6508 ± 1855 Present studySanta Luzia 28.1 ± 9.9 9.1 ± 1.7 5876 ± 2793 Present study

Monaco 25 ± 2 Miramand and Guary (1980)Eledone cirrhosa English Channel 6.0 ± 1.0 Miramand and Bentley (1992)Sepia officinalis English Channel 7.1± 0.2 Miramand and Bentley (1992)

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ACKNOWLEDGEMENTS

Staff at the Instituto Tecnólogico e Nuclear provid-ed assistance and facilities. The work was fundedunder grant number PRAXIS 2/2.1/MAR/1707/95.

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